PROJECT SUMMARY: Olfactory sensory losses, termed hyposmia or anosmia, are estimated to affect >12% of the US population. Common causes of acquired anosmias include aging-related declines (presbyosmia), post-viral olfactory disorder, trauma, inflammatory damage, or other idiopathic conditions. At present, there are no effective treatments for most of these conditions. A major barrier limiting the development of strategies to prevent or treat anosmias is our limited understanding of the precise pathogenesis. What are the cellular or molecular changes in the olfactory system associated with sensory loss? To address this issue, we propose experiments to apply the single cell RNA sequencing approach (scRNA-seq) to generate datasets defining the cell populations and states within adult human olfactory mucosa. Advances in droplet sequencing techniques have made such assays feasible, permitting the rapid analysis of >5000 cells from a small tissue sample. The olfactory mucosa in the nose is the peripheral organ for olfaction, housing the primary olfactory sensory neurons, related supporting populations, and basal stem cells supporting replacement of neuroepithelial cells as needed. We will focus attention to the olfactory mucosa, since this is (a) an accessible tissue in humans and (b) a likely site of pathology in many acquired anosmias. Using the scRNA-seq approach, we will develop single cell profiles from normosmic adults at young, middle or advanced age to develop comprehensive baseline data necessary for understanding the changes that occur in olfactory disorders. In contrast to existing reports, which are limited and largely descriptive, our proposed experiments will provide a quantitative atlas of the human olfactory mucosa. Using this approach, we will also examine the changes in the olfactory mucosa associated with presbyosmia, and examine whether this is consistent with a process involving neurogenic exhaustion. In addition, histologic samples will be prepared for the validation of gene expression patterns of specific interest, using antibodies or RNA in situ hybridization probes. We expect this R21 to provide baseline data enabling the future development of diagnostic and therapeutic strategies targeting molecular or cellular changes in the olfactory mucosa of human anosmic conditions.